You said it. You said the 318 has a slightly smaller bore. What matters is the bore to stroke ratio. A 318 will never have a B/S ratio of a 340. Neither will a 360.
While the numbers may look small, the ratio matters.
I did not say take a 318 over a 340.. i am also not the one that mentioned the bore.. we were talking about the value of 340s and the almost cult like worship that some give to it. Didn't say it was bad or better or worse than anything else.